input_file = ARGV[0]//前面说过ARGV就是个数组，应该知道这是取这个数组的每一个元素
def print_all(f)
  puts f.read()
end

def rewind(f)
  f.seek(0, IO::SEEK_SET)//搞清楚IO::SEEK_SET这是什么意思
end

def print_a_line(line_count, f)
  puts "#{line_count} #{f.readline()}"
end

current_file = File.open(input_file)

puts "First let's print the whole file:"
puts # a blank line

print_all (current_file)

puts "Now let's rewind, kind of like a tape."

rewind(current_file)

puts "Let's print three lines:"

current_line = 1
print_a_line(current_line, current_file)

current_line = current_line + 1
print_a_line(current_line,current_file)

current_line = current_line + 1
print_a_line(current_line, current_file)
#这些都还是比较简单的，我觉得可能你最需要分清楚的是方法定义和方法调用， 把这个搞清楚了， 看到哪些不同的名字的参数， 应该不会头晕
